Using DAQPad 6015 with Screw Terminations for Measuring Thermocouple TemperatureHardware: Multifunction DAQ (MIO)>>Basic>>DAQPad-6015 for USB
Problem: I have a DAQPad-6015 with screw-terminal connectors and I am trying to measure temperature using thermocouples. The collected data seems to stay accurate and stable for a while but after some time the data becomes very noisy and starts spiking to about 800 C. When I heat or cool the thermocouple, the readings return to their expected values. All of my connections are secure, so what could be causing this noise? Solution: Most often times, a thermocouple is a floating (nonreferenced) signal source. These types of signals can experience input bias currents when connected to instrumentation amplifiers; these bias currents can manifest as noise on the signal read by the instrumentation. To reduce this noise you can add resistors to connect the positive and negative terminals of the signal to the instrument ground. These resistors, called bias resistors, provides a DC path for the bias currents to ground. The DAQPad-6015 for USB with screw-terminal connectors does not have any built-in bias resistors, so you will need to manually connect resistors. Any resistor with a value between 1KΩ and 100KΩ should be sufficient, but the recommended value is a 5KΩ resistor in parallel with a 0.1µF capacitor. Related Links: Developer Zone Tutorial: Field Wiring and Noise Considerations for Analog Signals Attachments:
Report Date: 06/04/2006 Last Updated: 07/26/2007 Document ID: 3Y38L145 |
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